Load-transporting motor vehicles such as dump trucks, refuse trucks, transit concrete mixing trucks, open-bed trucks, utility trucks, military trucks and other vehicles of various types to which a significant load may be added for transport are limited in their load transporting ability by various factors. Such as the weight bearing capacity of their supporting axles and applicable federal and state law. With such laws for example limiting the gross vehicle weight to 80,000 pounds, the weight carried by a single axle to 20,000 pounds and there being an exception as to consecutive axles that limits them to carrying a prescribed combined weight depending on their number and spacing. For example, the combined axle carrying weight is limited to 34,000 pounds in regard to the two powered tandem axles that are typically employed with heavy duty load-transporting motor vehicles. And with such factors as a result impacting the use of load-transporting vehicles in that the more weight the vehicle can transport at a time, the more useful the vehicle can be provided other factors that impact the ability of the vehicle to perform in an acceptable manner are also taken into account. With such factors including the axle manufacturers rated load capacity.
And in regard to load-transporting motor vehicles that carry significantly heavy loads, they typically have primary axles that continuously support the vehicle and one or more auxiliary axles that are available to help support the vehicle in supporting such loads. Wherein the primary axles typically comprise a forwardly-located axle with steerable wheels and one or more rearwardly-located powered axles. And wherein the auxiliary axles are deployable and forcibly loaded to help carry the weight of the vehicle and thereby reduce the weight carried by the primary axles and are referred to as either a pusher axle, tag axle or trailing axle to distinguish between them. With the understanding that a pusher axle is suspended from the vehicle chassis in a location to operate between a forwardly located primary axle with steerable wheels and one or more rearwardly located powered axles with wheels and a tag axle is suspended from the vehicle chassis to operate rearward of one or more powered axles but not normally beyond the rear end of the chassis. Whereas a trailing axle that has also been referred to as a tag axle and trailing tag axle is also suspended from the vehicle chassis but in a manner to operate at a substantial distance rearward of the chassis.
Among the challenges faced in employing auxiliary axles, whether it is a pusher axle or a tag axle or a trailing axle, is in first determining whether auxiliary axle use is needed and then in determining the down force to be applied to the auxiliary axle(s) deployed and thereby the weight of the vehicle they carry. As this determines the extent to which the primary axles then carry the weight of the vehicle while also continuing to serve as intended with regard to vehicle performance such as in providing for suitable steerage, traction and braking.
For example and apart from servicing, if a trailing axle is deployed but is actually not needed for additional vehicle support, it should be sufficiently forced downward for trailing axle stability as otherwise it would be serving no useful purpose and could adversely affect the road performance of the vehicle. While on the other hand, if one or more auxiliary axles are deployed with the addition of a load and forced to support the vehicle weight necessary to meet restrictions governing the weights carried by the supporting axles and a maximum allowable gross vehicle weight, one or more of the primary axles while meeting the governing restrictions may be loaded beyond its maximum allowable carrying weight. Furthermore, when the wheels of an auxiliary axle that is acted on with a significantly low down force passes over sudden elevation changes such as in the case of a pothole or dip in a road surface, there are sudden dynamic forces that can result and are applied to the axle that may not be compatible with the structural design of the axle and its suspension. Moreover, in the case of a trailing axle there may be insufficient down force with regard to contributing to vehicle braking and roll stability as well as helping to support the vehicle.
Then at the other end of the spectrum, if one of the auxiliary axles whether it is a pusher axle or a tag axle or a trailing axle is down forced such that it accepts more vehicle weight than required to meet weight carrying limits on the primary axles, one or more of the latter may lose its ability to adequately perform as intended. For example, adequate steerage and braking at a forward-most primary axle with steerable wheels and adequate traction and braking at one or more rearward primary axles with powered wheels.
In addressing these concerns and viewing currently available load-transporting motor vehicles, most do not have onboard scales for determining the existing vehicle weight or the existing weight on each axle. And those that do typically have onboard scale systems that calculate and display the vehicle weight but not the weight on the individual axles.
And in the case where there is no onboard weight scale system and no weight scales where a load is being added to the vehicle, the vehicle operator is left with determining whether an auxiliary axle needs to be activated and thus depends on the experience of the vehicle operator and especially where there is more than one auxiliary axle available and thus involves needing to make a selection. And the experience of the vehicle operator may or may not extend to handling a particular type of load or various types of loads with different densities and in the manner they are received that may be wholly at one time at a site or with additional loading at another site that also lacks weight scales. Moreover, the choice of whether to activate or deactivate any auxiliary axles is made even more difficult where the vehicle for example makes multiples stops to either drop off part of a load or pick up additional load before reaching the final destination for off-loading.
Then in the case where the vehicle operator does recognize the need to activate one or more auxiliary axles based on experience or training or such is indicated by onboard weight scales or premeasured weights or weight scales at a pickup site, there remains the objective of tailoring the weight carried by an activated auxiliary axle in a significantly beneficial manner. As some auxiliary axles have only on/off capability wherein they apply a preset down force on the activated auxiliary axle that determines the amount of vehicle weight the axle carries/accepts. And this would require the vehicle operator to change the setting if possible for a particular weight if that appears to be needed from the standpoint of either increasing or decreasing the down force on a particular auxiliary axle and thereby the weight carried by this axle and resultantly the primary axle. But this is not a practical thing to do while on the road and in not knowing how much adjustment is actually needed for proper operation.
On the other hand and in the case where there is provided the ability to adjust the down force on the auxiliary axles when they are activated, the auxiliary axles are typically operated with a pressured system that applies a down force to the axle that determines the vehicle weigh it accepts. And the adjustment is typically provided by the vehicle operator observing a pressure gauge connected to the system and operating a control valve to adjust the system pressure relying on pressure readings indicative of the down force on the axle that results. But without knowing the current weight on an auxiliary axle or having some means to determine such, it is not known how much down force to add or subtract and again the vehicle operator is left with making that decision based on experience and/or training and doing the adjusting correctly. And even with a vehicle having onboard weight scales and providing the vehicle operator with the ability to adjust the down forces on the auxiliary axles as described above, these weight scales typically do not detect the weight on a deployed auxiliary axle such as a pusher axle, a tag axle and a trailing axle. And where there is more than one auxiliary axle, the vehicle operator may need to adjust them individually in ensuring that all the axles comply with certain applicable restrictions. And that requires the vehicle operator needing to know the applicable state and federal law that applies to both vehicle weight and the weight carried by the different axles and to then adjust each auxiliary axle as needed while calculating the vehicle weight on the various axles and though the vehicle with the available auxiliary axles deployed and loaded would appear to be in compliance with the applicable regulations, this could be a costly incorrect assumption.
Various approaches have been offered in addressing some of these challenges including the control system disclosed in U.S. Pat. No. 5,193,063 that is directed at load-transporting vehicles with one auxiliary axle and U.S. Pat. No. 6,371,227 that is directed at load-transporting vehicles with multiple auxiliary axles comprising pusher axles and a trailing axle. And while such control systems have addressed some of the challenges faced, there remains a desire for an automatic auxiliary axle control system that can deploy on actual need one or more auxiliary axles and then control the degree to which they help carry the weight of the vehicle in a manner such that all the axles supporting the vehicle are conditioned in so far as possible to efficiently meeting the operating objectives of the respective axles as well as complying with applicable state and federal law.